The present invention relates to photographic imaging, and more particularly to methods and apparatus for eliminating unwanted reflections in panoramic images.
Recent work has shown the benefits of panoramic imaging, which is able to capture a large azimuth view with a significant elevation angle. If instead of providing a small conic section of a view, a camera could capture an entire half-sphere at once, several advantages could be realized. Specifically, if the entire environment is visible at the same time, it is not necessary to move the camera to fixate on an object of interest or to perform exploratory camera movements. This also means that it is not necessary to actively counteract the torques resulting from actuator motion. Processing global images of the environment is less likely to be affected by regions of the image that contain poor information. Generally, the wider the field of view, the more robust the image processing will be.
A panoramic camera is a device that captures light from all directions (i.e., 360 degrees), either as still images or as a continuous video stream. The images from such a device can be geometrically transformed to synthesize a conventional camera view in any direction. One method for constructing a panoramic camera combines a curved mirror and an imaging device, such as a still camera or video camera. The mirror gathers light from all directions and re-directs it to the camera. Both spherical and parabolic mirrors have been used in panoramic imaging systems.
Numerous examples of such systems have been described in the literature. For example, U.S. Pat. No. 6,118,474 by Nayar discloses a panoramic imaging system that uses a parabolic mirror and an orthographic lens for producing perspective images. U.S. Pat. No. 5,657,073 by Henley discloses a panoramic imaging system with distortion correction and a selectable field of view using multiple cameras, image stitching, and a pan-flit-rotation-zoom controller.
Ollis, Herman, and Singh, xe2x80x9cAnalysis and Design of Panoramic Stereo Vision Using Equi-Angular Pixel Camerasxe2x80x9d, CMU-RI-TR-99-04, Technical Report, Robotics Institute, Carnegie Mellon University, January 1999, discloses an improved equi-angular mirror that is specifically shaped to account for the perspective effect a camera lens adds when it is combined with such a mirror.
Affixing the mirror to the camera is problematic, since any support structure must necessary appear in the device""s field of view. One approach is to use a center post to support the mirror. The center post approach leaves the curved mirror exposed to surface dirt. Furthermore, the center post support is inherently weak and prone to bending and optical misalignment. Finally, there is the issue of mounting it to the camera. There is no easy way to affix it to the camera other than boring through the camera""s lens or affixing the post to a transparent lens attachment.
Another approach is to make the support structure transparent, by using a glass or plastic cylinder that mounts onto a standard camera lens mount and supports the reflective surface. However, a xe2x80x9ctransparentxe2x80x9d material, such as glass or plastic, is typically not 100% transparent. Some light is not transmitted, but rather it is reflected off the surface of the glass or plastic. Light from the sun or another bright source can reflect off the interior surface of the material, strike the mirror, and reflect into the camera, producing a ghost image of the light source or a line of bright illumination called a flare.
U.S. Pat. No. 6,157,018 discloses an omnidirectional photographic device that uses a convex mirror and a camera coupled together by a transparent cylinder. A centrally mounted object is provided to eliminate rays of light that are internally reflected by the transparent cylinder. However, only internally reflected rays that pass through the axis of the cylinder are eliminated.
There is a need for a panoramic imaging system that provides an improved reduction in unwanted reflections in transparent mirror mounts.
A panoramic imaging system constructed in accordance with this invention comprises a convex reflector, a camera, a transparent cylinder for mounting the convex reflector to the camera, and a first radially-oriented planar member positioned in the transparent cylinder between the convex reflector and the camera. A second radially-oriented planar member can also be positioned in the transparent cylinder between the convex reflector and the camera. The first and second radially-oriented planar members would preferably lie in perpendicular planes, however, they may lie in non-perpendicular planes. Additional radially-oriented planar members can also be positioned in the transparent cylinder between the convex reflector and the camera. The radially-oriented planar members can each extend diametrically across the cylinder, and preferably include non-reflective surfaces.
The invention also encompasses a mirror mount for a panoramic imaging system comprising a convex reflector, a transparent cylinder for supporting the convex reflector, means for connecting a camera to the transparent cylinder, and a first radially-oriented planar member positioned in the transparent cylinder between the convex reflector and the camera. The mirror mount can further include a second radially-oriented planar member positioned in the transparent cylinder between the convex reflector and the camera. The first and second radially-oriented planar members would preferably lie in perpendicular planes, however, they may lie in non-perpendicular planes. Additional radially-oriented planar members can also be positioned in the transparent cylinder between the convex reflector and the camera. The radially-oriented planar members can each extend diametrically across the cylinder, and preferably include non-reflective surfaces.
The invention further encompasses a method of reducing unwanted reflections in a panoramic imaging system comprising the steps of mounting a convex reflector in a transparent cylinder, inserting a first radially-oriented planar member in the transparent cylinder, connecting a camera to the transparent cylinder, and using the camera to capture an image of a scene embodied in light reflected from the convex mirror. The method can further comprise the step of inserting a second radially-oriented planar member in the transparent cylinder between the convex reflector and the camera. The first and second radially-oriented planar members would preferably lie in perpendicular planes, however, they may lie in non-perpendicular planes. The cameras used in connection with this invention can be still or video cameras.